1. Field of the Invention
The present invention relates to a silicone elastomer porous body, and more specifically to a substantially closed-cell silicone elastomer porous body.
2. Description of the Related Art
Silicone elastomer porous bodies are used in a variety of fields, for example, as parts of image forming devices such as photocopiers and laser printers, including developing rollers, toner feeding rollers, transfer rollers and drum cleaning rollers, as sheet feeding rollers of photocopiers, various types of printers and plotters, and as pressure rollers of fixing devices.
Conventionally, porous bodies are produced mainly by utilizing foaming phenomenon. For foaming, a chemical foaming agent, a gas or water has been used as a foaming agent. The manufacture of silicone elastomer porous bodies is not exception, and in most cases, silicone elastomer porous bodies have been prepared by using one of these foaming agents. However, in such a conventional method of producing a silicone elastomer porous body, curing of silicone rubber and foaming are effected at simultaneously, with the result that cells (pores) in the resultant porous body are not uniform in size and their sizes vary in a wide range. Further, it is conventionally difficult to form cells having a small size.
On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 6-287348 discloses a method of producing a silicone elastomer porous body by freezing a room-temperature curing organopolysiloxane emulsion containing an organopolysiloxane having a silanol group, a specific crosslinking agent, a curing catalyst, and an emulsifying agent by refrigeration and sublimating the water to dry the frozen emulsion without defrosting it. Even with this method, it is still difficult to produce a porous body having uniform and fine cells. Further, the porous body obtained by this method is of an open cell type.
Silicone elastomer porous bodies that are produced using foaming agents have cells of large sizes that are uneven from cell to cell. With this structure, when heated, the shape of the porous body is not stable. In addition, when a torque is applied to the porous body, the force cannot be dispersed uniformly therethrough, and therefore the porous body is easily broken. Further, a porous body with large-sized cells entails such a drawback that when it is used for, for example, a pressure roller in an image forming device, the outlines of cells appear on the formed image. Furthermore, when the porous body is of an open cell type, the porous body is easily broken. Under these circumstances, there is a demand for a closed-cell silicon elastomer porous body having cells of a small and uniform size.